1. Field of the Invention
The present invention is directed to the field of fluid control valves and more particularly to that portion of the above-noted field which is concerned with acceleration (or deceleration) sensitive valve structures. As used throughout this specification, "acceleration" is to be understood to include increasing as well as decreasing velocity rate changes. Further, the present invention is directed to that portion of the above-noted field which is concerned with acceleration sensitive valves which may be arranged in a vehicle braking system specifically to sense rates of deceleration in order to modulate the deceleration rate. More particularly still, the present invention is directed to a deceleration rate sensitive valve and a brake system which will apply braking energy to maintain, upon command, a fixed maximum rate of deceleration and which will be fail safe to assure no loss of braking power to an associated vehicle. In light of the foregoing objective, it is a particular object of the instant invention to provide a damped deceleration sensitive valve for use in a vehicle braking system which may be made sensitive to a selected deceleration rate and which does not introduce fluid leakage problems.
2. Description of the Prior Art
It is known in the art to use a pendulum mounted to a rotatable shaft which, upon pendulous movement, will actuate the movable valve member of a fluid control valve. Such valve controls are frequently used in order to modulate fluid pressure or fluid flow in response to a rate of change of velocity with respect to time. Typically, such pendulums are supported in air externally of the valve mechanism. Control problems are known to exist with pendulum controlled fluid valves which respond to a pendulum supported in air.
The principal control problem of such devices is the result of difficulty of precise control of the amount of pendulum displacement. For example, such valves are subject to oscillatory movement under a variety of conditions. If such a valve is used as a fluid control valve, oscillations may cause undesired variations in the fluid control. The oscillations of an air supported pendulum can be of sufficiently great magnitude that fluid control will not be precise. In order to obtain precise fluid control, the undesired oscillations must be damped. Damping the oscillatory motion of a pendulum may be difficult because over-damping will result in slow pendulum response which may be highly undesirable in a fluid control system. Additionally, the movable valve member of such an apparatus provides an additional source of fluid leakage. In order to prevent fluid leakage, additional and expensive valve seals are required. In the event of fluid leakage the amount of control that such a device may provide is a variable.
A further problem with such devices is a result of the friction between the stationary valve components and the movable valve components which exists in any externally controlled valve structure. Since, as is well known, static and dynamic friction levels vary substantially, the action of such a valve as a deceleration control apparatus is such that abrupt changes in the deceleration rate will be generated. In order to reduce static friction, it is frequently the practice to employ very low friction bearings. However, such bearings ordinarily do not provide fluid sealing so that reduction of friction and fluid sealing have been mutually exclusive objectives in the prior art pendulum controlled fluid valves having reasonably low cost. It is therefore an object of the present invention to provide a pendulum actuated fluid control valve having improved fluid sealing and anti-friction characteristics.
It is known in the art that pendulum movement may be damped by way of resilient means or by suspending the pendulum in a fluid medium. While either approach to providing damping for the pendulum movement will substantially improve the predictability and control of valve movement, the aforenoted problems relating to the valve structure would require separate solution and added expense. For example, while it is possible that a substantial portion of the valve problems may be overcome by the use of relatively expensive and exotic sealing techniques, such a solution would unduly increase the cost and complexity of the resulting device without necessarily improving its reliability. It is therefore an object of the present invention to provide a velocity rate change sensitive fluid control valve which is relatively inexpensive and which may be reliable in operation. More specifically, it is an object of the present invention to provide an acceleration sensitive fluid valve which may be used in a vehicle braking system to reliably and safely limit maximum vehicle deceleration. It is also an object of the present invention to provide a fail-safe vehicle braking system utilizing such a valve. It is a further object of the present invention to provide an improved damped pendulum actuated fluid control valve having low friction which is not subject to fluid leakage adjacent relatively moving parts thereof. It is a further and specific object of the present invention to provide such a valve in which all moving parts are completely submerged in the fluid of the system and which does not require the transfer of motion from nonfluid contactive valve components to fluid contacting valve components.